Compositional Characteristics and Implications of Apatite in Rare‐Metal‐Bearing Pegmatites of the Himalayan Orogenic Belt, Southern Qinghai–Tibet Plateau

ABSTRACT This study focuses on apatites in rare‐metal‐bearing pegmatites of the Pusila, Kuqu, and Luozha regions of the Himalayan orogenic belt, and we systematically analyse their mineralogical and geochemical characteristics, as well as implications for petrogenesis and mineralization. All apatites are characterized by F enrichment and Cl depletion at grain margins, together with brighter cathodoluminescence along grain margins and fractures, recording a primary magmatic origin modified by later hydrothermal alteration. Apatites from Kuqu and Luozha fall within the S‐type granite field on discrimination diagrams. These grains host monazite inclusions and display seagull‐shaped REE patterns with extremely pronounced negative Eu anomalies and moderate Nd depletion, indicating an S‐type granitic parental source. Conversely, apatites from Pusila lack monazite inclusions and exhibit right‐inclined REE patterns with pronounced negative Eu anomalies and weak Nd depletion, implying a likely I‐type granitic parental source. Apatites from Pusila and Kuqu show no positive correlation among Sr, Ga, and δEu, and all samples plot within the moderately reduced field on the δEu–δCe diagram, indicating that the host pegmatites formed under moderately reducing conditions. All apatites display markedly increasing X F /X OH and X F /X Cl ratios but decreasing X Cl /X OH ratios, with compositional trends evolving toward the X F –X OH binary join, consistent with crystallization during magmatic fluid saturation and exsolution. Combined with pegmatite petrogenesis and the high‐F (averaging 1.98–2.24 wt%) and low‐Cl (averaging 0.01–0.08 wt%) compositions of these apatites, we propose that extensive fractional crystallization coupled with F complexation–migration promoted rare‐metal mineralization.